1. Field of the Invention
The present invention relates to a discharge bulb having an arc tube that is a sealed bulb acting as a light-emitting discharge section formed with pinch seal portions on both ends thereof.
2. Description of the Related Art
A conventional discharge bulb is illustrated in FIG. 9. A cylindrical shroud glass 3 having an ultraviolet blocking effect is integrally welded to an arc tube 1. The cylindrical shroud glass 3 covers pinch seal portions 1a and 1b and a sealed glass bulb 2 that is a light-emitting discharge section. The cylindrical shroud glass 3 is used, in part, to prevent broken pieces of the arc tube 1 from spreading as a result of an explosion, and to eliminate ultraviolet light in a waveband that is harmful to human bodies and the like from the light emitted by the sealed glass bulb 2. The reference symbol xe2x80x9caxe2x80x9d represents electrodes provided in a face-to-face relationship with the sealed glass bulb 2 as a light-emitting section, and the reference symbol xe2x80x9cbxe2x80x9d represents molybdenum foils sealed to the pinch seal portions 1a and 1b. The electrodes a and a and the lead wire c are connected to the molybdenum foil b.
The lead wire c extracted from the pinch seal portion 1a on the front end of the arc tube 1 is supported by a lead support 6 extending in front of an insulated base 5, and the rear end of the arc tube 1 is secured to the front side of the insulated base 5 with an adhesive 4 to integrate the arc tube 1 with the insulated base 5.
The symbol 10 represents a reflector for forming a meeting beam from, for example, a headlamp of an automobile, and symbol 9 represents a shade having a light-blocking section in a configuration adapted to an effective reflecting surface 10a of the reflector and is typically provided to guide light emitted by the sealed glass bulb 2 only to the effective reflecting surface 10a. The shade 9 also has a function of forming clear-cut lines of a luminous distribution pattern.
In the above-described conventional discharge bulb, since a very large quantity of light is emitted by the sealed glass bulb 2 compared to an incandescent light, a large quantity of light is also guided to the pinch seal portions because of a light-guide effect. For reasons including the fact that the molybdenum foils b that reflect light are normally provided on the pinch seal portions 1a and 1b, and that the surface configuration of the pinch seal portions is uneven, light can exit the pinch seal portions 1a and 1b and be reflected by the reflector 10 in the forward direction, which could result in glare.
In an intention to prevent light from exiting the pinch seal portions 1a and 1b, the inventors applied light-blocking films, that had generally been used for forming a luminous distribution, to the pinch seal portions 1a and 1b and to the shroud glass 3. However, using this technique, new problems arose in that an intended color temperature could not be achieved because of a large increase of the temperature of the pinch seal portions 1a and 1b and the sealed glass bulb 2, although light from the pinch seal portions 1a and 1b is prevented to some degree. In addition, the pinch seal portions 1a and 1b become likely to crack which reduces the durability of the arc tube. Further, the light-blocking films can come off because of the high temperature in their environment.
The inventors thought that the great increase in the temperature of the arc tube was attributable to the fact that the conventional light-blocking films for forming a luminous pattern blocked infrared light in addition to visible light to accumulate heat in the arc tube. Then, they thought that the accumulation of heat in the arc tube could be avoided by transmitting infrared light while blocking visible light. In experiments, the inventors confirmed that the above-described problems will not occur when infrared transmitting films for blocking visible light and transmitting infrared light are used as the light-blocking films to prevent the overheating of the pinch seal portions 1a and 1b and the sealed glass bulb 2, and accordingly, the present invention is being presented based on such a finding.
It is an object of the present invention to provide a discharge bulb that does not produce glare and that has excellent durability by applying infrared transmitting films for blocking visible light and transmitting infrared light to at least pinch seal portions of an arc tube.
In order to achieve the above-described object, a discharge bulb according to a first aspect of the invention includes an arc tube that is a sealed bulb, for example, a glass bulb, as a light emitting discharge section formed with pinch seal portions at both ends thereof, in which infrared transmitting films for blocking visible light and transmitting infrared light are applied to at least the pinch seal portions of the arc tube.
The infrared transmitting films prevent visible light from exiting the pinch seal portions, and therefore suppress generation of light that can result in glare.
Since the infrared transmitting films do not prevent infrared light from exiting the pinch seal portions, no heat is accumulated in the arc tube (in particular, the pinch seal portions and sealed glass bulb).
In a second aspect of the invention, the arc tube of the present invention may be provided in a lighting chamber of a vehicle front light lamp, and the infrared transmitting films may be applied in predetermined ranges extending from the bottom of the sealed glass bulb of the arc tube provided in the lighting chamber to left and right lateral surfaces thereof.
Since substances such as mercury and a metal halide may be enclosed in the sealed glass bulb in a saturated state, the enclosed substances may be deposited in a liquid state on the bottom of the sealed glass bulb. As a result, light exiting the sealed glass bulb downward becomes yellow light that is colored by the enclosed substances, and that light is mixed with white light that should be emitted by the sealed glass bulb, which is not preferable. The infrared transmitting films provided to extend from the bottom of the sealed glass bulb to left and right lateral surfaces thereof prevent the colored light (yellow light) from exiting the sealed glass bulb.
In a third aspect of the present invention, the discharge bulb may be an arc tube that has a sealed glass bulb as a light emitting discharge section formed with pinch seal portions on both ends thereof and a cylindrical shroud glass integrally joined, such as by welding, to the arc tube to enclose and seal the arc tube. Infrared transmitting films for blocking visible light and transmitting infrared light are applied to at least the pinch seal portions of the arc tube and/or at least regions of the shroud glass associated with the pinch seal portions.
The infrared transmitting films provided on the pinch seal portions of the arc tube and/or the shroud glass prevent visible light from exiting the pinch seal portions and prevent visible light that has exited the pinch seal portions from exiting the shroud glass, which suppresses generation of light that can result in glare.
The infrared transmitting films provided on the pinch seal portions of the arc tube and/or the shroud glass do not prevent infrared light from exiting the pinch seal portions and do not prevent infrared light that has exited the pinch seal portions from exiting the shroud glass, which prevents accumulation of heat in the arc tube (the pinch seal portions and sealed glass bulb).
Especially, when the infrared transmitting film is applied only to the shroud glass, accumulation of heat in the arc tube is less likely to occur than when the infrared transmitting film is applied to the pinch seal portions only or to both of the pinch seal portions and the shroud glass because the temperature of the shroud glass is lower than the temperature of the arc tube (pinch seal portions) when the discharge bulb is turned on.
When the infrared transmitting film is applied to both of the pinch seal portions and shroud glass, visible light is prevented from exiting two times, which reliably prevents generation of light that can result in glare.
Further, in a discharge bulb according to a fourth aspect of the present invention, the arc tube may be provided in a lighting chamber of a vehicle headlamp, and the infrared transmitting films are applied in predetermined ranges extending from the bottom of the sealed glass bulb of the arc tube provided in said lighting chamber to left and light lateral surfaces thereof and/or in predetermined ranges extending from the bottom of the shroud glass to left and right lateral surfaces thereof.
Since substances such as mercury and a metal halide are enclosed in the sealed glass bulb in a saturated state, the enclosed substances are deposited on the bottom of the sealed glass bulb in a liquid state. As a result, light exiting the sealed glass bulb downward becomes yellow light that is colored by the enclosed substances, and the light is mixed with white light that should be emitted by the sealed glass bulb, which is not preferable. The infrared transmitting film on the bottom of the sealed glass bulb and/or the bottom of the shroud glass prevents the colored light (yellow light) from exiting the sealed glass bulb and/or shroud glass.
In a fifth aspect of the invention, the discharge bulb may be used as a light source of a reflection type headlamp for forming a predetermined luminous distribution with light reflected by a reflector provided behind the same. Infrared transmitting films to serve as linear light-blocking sections for forming clear-cut lines of the luminous distribution pattern are applied to left and right lateral surfaces of the shroud glass.
Since clear-cut lines of a luminous distribution pattern are formed by the linear light-blocking sections extending before and behind the infrared transmitting films applied to the left and right lateral surfaces of the shroud glass form clear-cut lines of a luminous distribution pattern, there is no need for a shade for forming clear-cut lines.
Further, in a sixth aspect of the invention, the linear light-blocking sections for forming clear-cut lines provided on the left and right lateral surfaces of the shroud glass are constituted by infrared light/visible light blocking films extending in the form of strings.
A luminous distribution having sharp clear-cut lines can be formed by forming the linear light-blocking sections for forming clear-cut lines of a luminous distribution pattern using infrared light/visible light blocking films which can be formed with high accuracy compared to infrared transmitting films.
In a seventh aspect of the invention, the discharge bulb may be used as a light source of a reflection type headlamp for forming a predetermined luminous distribution with light reflected by a reflector provided behind the same. Infrared transmitting films applied to the shroud glass are applied in regions of the shroud glass other than a region associated with an effecting reflecting surface of said reflector contributing to the formation of the luminous distribution.
Visible light included in light exiting the sealed glass bulb that is a light-emitting discharge section passes through regions of the shroud glass where the infrared transmitting films are not applied, and it is reflected forward by the effective reflecting surface of the reflector to form a predetermined luminous distribution. Infrared light included in the light exiting the sealed glass bulb that is a light-emitting discharge section exits the shroud glass in all regions thereof without being blocked by the infrared transmitting films on the shroud glass, which improves radiation of the arc tube.